This research project deals with the role of the intestinal mucosa in the regulation of sterol metabolism in experimental animals and in man. Specifically, it is proposed to investigate: 1) Properties and subcellular distribution of enzymes which are likely to be rate-limiting in sterol biosynthesis, e.g. HMG CoA reductase, HMG CoA synthase, HMG CoA lyase. 2) The activities of these enzymes as affected by the magnitude, circulation rate and composition of the bile acid pool, cholesterol, other sterols, drugs, hormones and diet. 3) The relationship between intestinal sterol synthesis and the cholesterol/bile acid balance of the intact organism.